The present invention relates to a combustion-type power tool, and more particularly, to such power tool having an improved motor mount structure.
In a conventional combustion-type driving tool such as a nail gun, a gaseous fuel injected into a combustion chamber is ignited to cause gas expansion in the combustion chamber, which in turn causes a linear momentum of a piston. By the movement of the piston, a nail is driven into a workpiece. In order to improve combustion, a fan is disposed in the combustion chamber for agitating a combustible gas. Such conventional combustion-type driving tool is disclosed in U.S. Pat. Nos. 4,483,280, RE 32,452 and 5,197,646.
A rotation drive unit such as a motor is disposed in a frame of the driving tool for rotating the fan. By the rotation of the fan, a turbulent flow is generated in the combustion chamber to promote combustion within the combustion chamber. Thus volumetric expansion occurs in the combustion chamber which in turn occurs impact. The impact is propagated to an entirety of the tool. Thus, the motor is also subjected to impact force.
In case of the combustion type fastener driving tool, the volumetric expansion generates movement of the piston for driving the fastener at the time of combustion. Surplus energy of the piston is absorbed at a bumper disposed within and one end of a cylinder in which the piston is slidingly moved. Acceleration is imparted to the entirety of the driving tool when the piston impacts against the bumper, and this acceleration is also transmitted to the motor.
Generally, the motor is not a shock proof precision instrument. Therefore, performance of the motor may be lowered due to structural damage caused by the repeated application of impact or shock, and finally the motor may be destroyed. To avoid this drawback, U.S. Pat. No. 6,520,397 discloses a cushioning member interposed between an outer frame and the motor so as to protect the motor against the shock. Thus, moderated shot transmission to the motor results.
More specifically, as shown in FIGS. 6 and 7, a combustion type fastener driving tool 101 includes a housing 102 having an upper end provided with a head cap 111 covered by a head cover 103. A motor 118 is supported to the housing 102 through the head cap 111. The motor 118 includes a motor case 118a serving as an outer casing, and a motor shaft 118b, and a fan 119 is fixed to a tip end of the motor shaft 118b. Further, an ignition plug 112 protruding into a combustion chamber 126 is supported to the head cap 111 at a position adjacent to the motor 118.
A pair of annular grooves are formed at an outer peripheral surface of the motor case 118a. The annular grooves are spaced away from each other in an axial direction of the motor case 118a. As shown in FIG. 6, retaining rings 114 are fitted into the pair of annular grooves, and an inner ring 113a which is a constituent of a suspension member 113 is interposed between the retaining rings 114, 114.
As shown in FIG. 7, the suspension member 113 includes the inner ring 113a, an outer fixing metal 113c and a rubber member 113b fixed between the inner ring 113a and the fixing metal 113c by baking. The fixing metal 113c is fixed to the head cap 111. Thus, the motor 118 is connected to the head cap 111 through the suspension member 113.
If the driving tool 101 is subjected to impact force, the impact is transmitted to the fixing metal 113c, but is moderately transmitted to the inner ring 113a and to the motor 118 because of the damper effect of the rubber member 113b. 